Notice: Undefined variable: metabox_feat_img

Hello. I recently added a shortcode to display blog posts in my websites front page, and when the post is clicked, this message pops up: "Notice: Undefined variable: metabox_feat_img in /home/vol9_4/byethost10.com/b10_17487215/htdocs/wp-content/themes/parallax-frame/inc/core.php on line 1302" You can see it yourself here: http://paulinasjoberg.com/hello-world/ When I go to the 1302nd line in core.php, this is what I see: if ( 'default' == $metabox_feat_img ) { I'm not too tech savvy with code, and id love if you could help me figure out how to fix this error. Thank you!